末次盛冰期和全新世大暖期新疆地区沙漠边界移动初探

位于新疆地区的塔克拉玛干沙漠、库姆塔格沙漠和古尔班通古特沙漠是我国沙漠的重要组成部分,它们在末次盛冰期以来的空间变化受气候影响[1-3].本文基于野外观察分析,结合实测数据和前人的研究资料,尝试重建这3个沙漠在末次盛冰期(LGM)和全新世大暖期(HO)的空间变化.沙漠边界内外有确定测年的晚第四纪沉积,尤其是含有风成沙、黄土的沉积序列,是指示沙漠扩张和收缩的重要标志[1-4].可以认为,在现代沙漠边界外围LGM时期的风成沙往往是沙漠扩张的证据;在现代边界内HO时期的黄土堆积往往揭示了沙漠收缩与沙丘固定.     

甘孜绒坝岔古冰川演化与黄土古土壤对比研究

横断山脉绒坝岔，保留有从倒数第二次冰期到新冰期的较完整的冰川沉积序列。对冰碛物进行了ESR测年，其分别形成于5．6kaBP、新冰期与末次冰期之间、16．3kaBP、18．7kaBP、43．7kaBP以及倒数第二次冰期。TL测年结果显示，甘孜雅砻江江畔阶地黄土从末次冰期之初开始堆积，结合甘孜黄土-古土壤序列代用指标的综合分析，发现绒坝岔冰碛物形成年代与甘孜剖面黄土、古土壤沉积年代有较好的对应关系。末次冰盛期(LGM)，绒坝岔冰碛垄走向有一次接近90。的改变；末次冰期间冰段，对应于MIS3b，其冰川规模甚至超过了LGM时期。     

晚更新世末期东海北部古冬季风盛衰变更的地质记录

末次冰期最盛时期,干、冷气候盛行,渤海、黄海的大部分地区出现沙漠化,形成众多的沙丘。随着干冷气候的减弱,长江三角洲一带出现硬粘土沉积。冰消期的到来,古季风活动的进一步衰退和海面的不断升高,来自陆架区的东北风不再是干冷的气流,而是湿度逐渐增大的冷湿气流,出现了有利于沼泽发育的环境,以致全新世海侵前夕往往形成薄层泥炭沉积。晚更新世末期以来古冬季风发生、发展和衰退过程与沙漠、硬粘土和泥炭层形成过程相对应。      

末次冰期晚期半干旱环境下黄河阶地上的河流与风沙沉积交互过程

风沙与河流地貌过程的交互作用是半干旱环境典型的地表过程。位于半干旱区的黄河兰州至银川段,现代风沙与河流沉积过程相互影响剧烈,而该区域地质历史时期风沙与河流交互过程的沉积记录还鲜有报道。文章对该区域黄河二级河流阶地堆积序列(河道砾石-具水平层理砂层-沙丘砂-条带状粉砂)进行了详细的沉积学分析。结果表明,流水作用形成的水平砂层之上覆盖的厚2~3.8 m的沙丘,由成分均匀的极细砂和粗粉砂组成;发育块状结构,而未见流水沉积结构;为典型风成沙丘。其上覆盖的粉砂层,粒度组成与该地区砂质黄土有相似性,以粗粉砂颗粒为主;但其还含有少量的粘土和极细砂组分,分选差,且发育薄层条带状纹层(层厚约5~10 cm);为河漫滩环境下主要为风尘输入的颗粒在静水条件下沉降形成的河漫滩相沉积。风成沙丘的众数粒度值略小于下伏水平状河流砂众数粒度,而粗颗粒组分和细颗粒组分含量都略小于下伏河流砂,表明风成沙丘可能是由风力分选、搬运下伏河流砂,就地堆积形成。风成沙丘与下伏河流砂的主量元素组成基本一致,而与该区域物质来源于较大范围的风成砂黄土主量元素的组成相差较远,也表明该阶地堆积序列中发育的风成沙丘物质来源于局地下伏的河流砂层。光释光年代测试的结果表明,风成沙丘堆积于距今约21~16 ka期间,而上覆河漫滩堆积于距今约14~13 ka期间。末次盛冰期,干旱气候和强劲的冬季风导致早期河漫滩上发育风成沙丘,而随后的冰消期夏季风的加强和相对暖湿的气候,使得末次盛冰期形成的沙丘被河漫滩沉积覆盖。该区域黄河二级阶地由辫状河砾石(夹砂透镜体)-河漫滩砂-风成沙丘-河漫滩粉砂构成的沉积序列是该区域末次盛冰期以来风沙与河流交互作用形成的良好记录,反应了半干旱地区地表过程(风沙和河流交互)对气候环境变化的响应。     

末次盛冰期以来长江南通段古河谷的地层特征

通过对南通段古河谷典型钻孔及剖面沉积物颗粒、微体生物化石、14C测年等的分析,对末次盛冰期以来的沉积地层进行了划分。该段古河谷末次冰期以来的地层,基本上反映了河床相—河漫滩相—浅海相—三角洲相的冰后期海侵沉积旋回。现代河床的底部,浅海相淤泥质亚黏土层已被侵蚀掉,沉积的是现代河床相砂层。     

中国中原末次冰期中晚期季风变化

中国中原邙山黄土晚更新世以来的沉积序列是迄今为止陆地上发现的最快速沉积之一,它为研究过去的气候变化提供了重要依据。末次冰期中晚期以来中原黄土磁化率及>45μm粗颗粒含量曲线显示东亚冬夏季风均呈高频率高振幅的变化。在万年尺度的冬夏季风变迁的相互关系上,夏季风强盛基本上对应于冬季风衰弱。在末次冰期间冰阶时期及全新世时期,东     

晚更新世末期中国北方陆架区冰缘现象的发现

末次冰期极盛期,海面下降,陆架裸露。寒流爆发南下,使亚洲东部平原区比世界同纬度地区的气温低。强寒流的侵袭,使海退后的陆架平原成为我国东部冰缘地貌的形成区之一。陆架上的冰缘地貌包括:大面积分布的沙地、成群出现的沙丘、零散分布的塌陷沉积、类似揉皱现象的波状夹层、频频出现的冰楔等。      

光释光测年揭示的科尔沁沙地末次晚冰期-全新世沙漠空间格局变化

对中国东北地区科尔沁沙地13个风成沙剖面和3个黄土剖面进行了研究,测试分析了黑色砂质土壤和下伏古风成沙的OSL年龄及粒度、磁化率、色度数据;OSL测年获得的古风成沙数据位于末次冰期晚期-全新世期间(13 ～1Oka),小于26.5 ～19.Oka的末次冰盛期时段.末次冰盛期干冷气候背景下沙丘持续不断的活化翻动,风成沙在进入全新世气候转暖后才被固定,沙地内全新世黑色砂质土壤下伏的疏松流沙为末次冰盛期产物,其分布范围可代表末次冰盛期流动沙丘的分布范围.现今科尔沁沙地面积约为42000km2,活动沙丘面积约占10％.在末次冰盛期不仅原固定沙丘活化,沙质平原与部分甸子也被流沙覆盖,面积约85000km2,活动沙丘或流沙面积相对目前扩大了约20倍.末次冰盛期沙地活化扩张的控制因素主要有两方面:一方面冰期气候干旱寒冷,降水减少,地表植被覆盖下降,地表松散沉积物遭受风力剥蚀而活化成流沙;另一方面科尔沁沙地内部水系发育,河流流经途中会沉积大量松散物质.在冰期干冷环境下,河流水位下降,河流沙暴露并遭受风蚀改造,为流沙扩张提供物源,沙漠沿西拉木伦河流域扩展.     

冲绳海槽的晚第四纪浊流沉积

冲绳海槽晚第四纪的浊流沉积发育在海底斜坡带和坡折处静水环境,属阵发性纵向浊流。物质来源于海槽中心斜坡区的滑塌沉积物、岛坡、陆坡和台湾宜兰浇滩的碎屑沉积物。受控于海底地形、滞流环境和构造岩浆活动以及伴生的浅源地震。 冲绳海槽海底表层浊流沉积物,形成在晚更新世末次冰期最盛期、末次冰期末和冰后期三个阶段,以末次冰期最盛期阵发频繁,浊积物最发育,与气候寒冷期有一定的相关性。     

南海深水区晚更新世以来沉积速率、沉积通量与物质组成

通过调查所获得柱样沉积物氧碳同位素测年资料及多学科综合分析表明,晚更新世以来南海沉积速率和沉积通量具有以下几个特征 :(1)总体上为间冰期沉积速率低、冰期沉积速率高,冰期沉积速率是间冰期沉积速率的 1.3～ 1.6倍;(2 )南海沉积速率趋势面分析表明,氧同位素 1期东北陆坡和西南陆坡沉积速率高,氧同位素 2、3期沉积速率分布特征相似,与 1期有所不同,东北陆坡沉积速率高于西南陆坡,表明氧同位素 2期之后,南海的沉积环境发生明显的改变,造成上述沉积速率分布的主要控制因素是南海周围的河流分布、季风、海流等;(3)南海东部沉积通量与物质组成分析表明,末次冰期以来沉积总通量北部陆坡区明显高于深海区,前者是后者 2～ 3倍,并有自北向南逐渐降低的趋势;(4)硅质生物沉积通量冰期明显高于间冰期,末次冰期以来东北部陆坡区的硅质生物沉积通量最高,末次冰期之前恰好相反,深海盆高于陆坡区;(5 )末次冰期以来,陆源沉积约占南海东部海域沉积的 4 4 %以上。     

The action of wind and water in a mid‐Cretaceous subtropical erg‐margin system close to the Variscan Iberian Massif,Spain

Aeolian processes and ephemeral water influx from the Variscan Iberian Massif to the mid‐Cretaceous outer back‐erg margin system in eastern Iberia led to deposition and erosion of aeolian dunes and the formation of desert pavements. Remains of aeolian dunes encased in ephemeral fluvial deposits (aeolian pods) demonstrate intense erosion of windblown deposits by sudden water fluxes. The alternating activity of wind and water led to a variety of facies associations such as deflation lags, desert pavements, aeolian dunes, pebbles scattered throughout dune strata, aeolian sandsheets, aeolian deposits with bimodal grain‐size distributions, mud playa, ephemeral floodplain, pebble‐sand and cobble‐sand bedload stream, pebble–cobble‐sand sheet flood, sand bedload stream, debris flow and hyperconcentrated flow deposits. Sediment in this desert system underwent transport by wind and water and reworking in a variety of sub‐environments. The nearby Variscan Iberian Massif supplied quartzite pebbles as part of mass flows. Pebbles and cobbles were concentrated in deflation lags, eroded and polished by wind‐driven sands (facets and ventifacts) and incorporated by rolling into the toesets of aeolian dunes. The back‐erg depositional system comprises an outer back‐erg close to the Variscan highlands, and an inner back‐erg close to the central‐erg area. The inner back‐erg developed on a structural high and is characterized by mud playa deposits interbedded with aeolian and ephemeral channel deposits. In the inner back‐erg area ephemeral wadis, desiccated after occasional floods, were mud cracked and overrun episodically by aeolian dunes. Subsequent floods eroded the aeolian dunes and mud‐cracked surfaces, resulting in largely structureless sandstones with boulder‐size mudstone intraclasts. Floods spread over the margins of ephemeral channels and eroded surrounding aeolian dunes. The remaining dunes were colonized occasionally by plants and their roots penetrated into the flooded aeolian sands. Upon desiccation, deflation resulted in lags of coarser‐grained sediments. A renewed windblown supply led to aeolian sandsheet accumulation in topographic wadi depressions. Synsedimentary tectonics caused the outer back‐erg system to experience enhanced generation of accommodation space allowing the accumulation of aeolian dune sands. Ephemeral water flow to the outer back‐erg area supplied pebbles, eroded aeolian dunes, and produced hyperconcentrated flow deposits. Fluidization and liquefaction generated gravel pockets and recumbent folds. Dune damming after sporadic rains (the case of the Namib Desert), monsoonal water discharge (Thar Desert) and meltwater fluxes from glaciated mountains (Taklamakan Desert) are three potential, non‐exclusive analogues for the ephemeral water influx and the generation of hyperconcentrated flows in the Cretaceous desert margin system. An increase in relief driven by the Aptian anti‐clockwise rotation of Iberia, led to an altitude sufficient for the development of orographic rains and snowfall which fed (melt)water fluxes to the desert margin system. Quartzite conglomerates and sands, dominantly consisting of quartz and well‐preserved feldspar grains which are also observed in older Cretaceous strata, indicate an arid climate and the mechanical weathering of Precambrian and Palaeozoic metamorphic sediments and felsic igneous rocks. Unroofing of much of the cover of sedimentary rocks in the Variscan Iberian Massif must therefore have taken place in pre‐Cretaceous times.     

Amalgamated accumulations resulting from climatic and eustatic changes, Akchar Erg, Mauritania

The Akchar Erg of the Sahara of western Mauritania shows a morphology and stratigraphy that can be recognized as the amalgamation of late Pleistocene and Holocene deposits that reflect eustatic and climatic events. Mapping, trenching, and dating by ¹⁴C methods and artefacts show that the prominent complex linear dunes (draas) of the Akchar Erg are actually composite features showing at least three constructional and two destructional phases. The constructional phases are represented by three convex-up layers: (i) a modern veneer moulded into superimposed crescentic dunes, which partially mantle the larger linear bedforms; (ii) a middle, partly root-turbated sand deposited sometime during the last 4000 years; and (iii) a core of linear dune sand formed during the last glacial period (13 000–20 000 yr BP), which today shows relict relief, intense root-turbation, and pedogenesis. These constructional phases are separated by super bounding surfaces that coincide with erg destructional phases. Surface 2 bounds the middle aeolian sand, and is marked by a lag surface of small granules. Surface 1 is a very prominent surface with an abundance of Neolithic artefacts, and represents stabilization of the linear dunes during the humid, interglacial period (4000–11 000 yr BP). Interdraa deposits originated during the interglacial period, and consist of continental lacustrine limestones and sandstones, humic sands deposited in marshes, and sabkhas on the coast. The sabkhas originated during interglacial highstand of sea-level when interdraa areas were marine embayments, and subsequently dried during regression. The draa and interdraa sequences, therefore, in spite of being adjacent facies, actually represent different events and were not formed simultaneously. The upwind sand-sheet margin of the Akchar Erg shows exposures of the middle and core aeolian sands (which were previously protected from deflation by vegetation) being progressively cannibilized in the current phase of erg construction, and revealing a crystalline basement rock. In this proximal area, conditions are not favourable for the incorporation of these aeolian accumulations into the stratigraphic record.     

Why deposits of longitudinal dunes are rarely recognized in the geologic record

Dunes that are morphologically of linear type, many of which are probably of longitudinal type in a morphodynamic sense, are common in modern deserts, but their deposits are rarely identified in aeolian sandstones. One reason for non-recognition of such dunes is that they can migrate laterally when they are not exactly parallel to the long-term sand-transport direction, thereby depositing cross-strata that have unimodal cross-bed dip directions and consequently resemble deposits of transverse dunes. Dune-parallel components of sand transport can be recognized in ancient aeolian sands by examining compound cross-bedding formed by small dunes that migrated across the lee slopes of large dunes and documenting that the small dunes migrated with a component in a preferred along-crest direction over the large dunes.     

Aeolian sand sea development along the mid‐Cretaceous western Tethyan margin (Spain): erg sedimentology and palaeoclimate implications

The existence of a mid‐Cretaceous erg system along the western Tethyan margin (Iberian Basin, Spain) was recently demonstrated based on the occurrence of wind‐blown desert sands in coeval shallow marine deposits. Here, the first direct evidence of this mid‐Cretaceous erg in Europe is presented and the palaeoclimate and palaeoceanographic implications are discussed. The aeolian sand sea extended over an area of 4600 km². Compound crescentic dunes, linear draa and complex aeolian dunes, sand sheets, wet, dry and evaporitic interdunes, sabkha deposits and coeval extradune lagoonal deposits form the main architectural elements of this desert system that was located in a sub‐tropical arid belt along the western Tethyan margin. Sub‐critically climbing translatent strata, grain flow and grain fall deposits, pin‐stripe lamination, lee side dune wind ripples, soft‐sediment deformations, vertebrate tracks, biogenic traces, tubes and wood fragments are some of the small‐scale structures and components observed in the aeolian dune sandstones. At the boundary between the aeolian sand sea and the marine realm, intertonguing of aeolian deposits and marine facies occurs. Massive sandstone units were laid down by mass flow events that reworked aeolian dune sands during flooding events. The cyclic occurrence of soft sediment deformation is ascribed to intermittent (marine) flooding of aeolian dunes and associated rise in the water table. The aeolian erg system developed in an active extensional tectonic setting that favoured its preservation. Because of the close proximity of the marine realm, the water table was high and contributed to the preservation of the aeolian facies. A sand‐drift surface marks the onset of aeolian dune construction and accumulation, whereby aeolian deposits cover an earlier succession of coastal coal deposits formed in a more humid period. A prominent aeolian super‐surface forms an angular unconformity that divides the aeolian succession into two erg sequences. This super‐surface formed in response to a major tectonic reactivation in the basin, and also marks the change in style of aeolian sedimentation from compound climbing crescentic dunes to aeolian draas. The location of the mid‐Cretaceous palaeoerg fits well to both the global distribution of other known Cretaceous erg systems and with current palaeoclimate data that suggest a global cooling period and a sea‐level lowstand during early mid‐Cretaceous times. The occurrence of a sub‐tropical coastal erg in the mid‐Cretaceous of Spain correlates with the exposure of carbonate platforms on the Arabian platform during much of the Late Aptian to Middle Albian, and is related to this eustatic sea‐level lowstand.     

Study of Sand Dunes and Their Effect on Desertification of Cultivated Lands in Shaanxi Province, China Using Remote Sensing Techniques

About half of the arid and semi-arid lands in the world are deserts that comprise various types of aeolian sand dunes deposits. In Shaanxi Province, aeolian sand dunes cover considerable areas of the Yulin desert and northern Jinbian. Sand dunes are moving in the main wind direction and converting some agricultural area to wasteland. Remote sensing of sand dunes helps in the understanding of aeolian process and desertification. Remote sensing data combined with field studies are valuable in studying sand dunes, regional aeolian depositional history. In particular, active and inactive sand dunes of the north Shaanxi Province were studied using remote sensing and geographic information system. In this study, we describe the Landsat thematic mapper (TM) images, covering north Shaanxi Province, which were used to study the distribution, shape, size, trends, density and movement of sand dunes and their effect on desertification of cultivated lands. Estimation was made depending on soil erodibility factor (Ⅰ) and local climatic factor (C) during the period (June to September). The result indicates that soil erosion caused sand drift of 8.957 5, 7.03 ton for Yulin and Jinbian, respectively. The mean sand dunes movement rate were 4.37, 3.11 m, whereas, monthly sand dune advance rate were 1.092 5, 0.777 5 m, for the two locations, respectively. The study reveals that cultivated lands extended obliquely to the direction of sand dune movement are extremely affected, while other segments that extend parallel to the direction of the movement are not affected. Accordingly the north Shaanxi Province was divided into areas of different classes of potential risk. Moreover, blown sands and sand movement from neighboring highlands also affect the area of western desert.     

基于扫描电镜分析的猪野泽全新世砂层成因探讨

猪野泽全新世沉积物剖面中存在砂层和灰绿色湖相沉积层相间分布的现象。本研究对猪野泽QTH01、QTH02剖面砂层的石英砂样品进行扫描电镜分析,且与古湖泊岸堤和现代沙丘砂样做了对比,探讨了猪野泽全新世剖面中部和底部砂层的成因。研究发现,猪野泽QTH01、QTH02剖面样品中大部分石英砂兼具风成结构和水成结构,且水成特征大都覆盖于风成特征之上,V型坑分布频率相对较小,磨圆度特征与现代沙丘样品较为相似,与岸堤石英砂具有相似的结构特征,但剖面砂层不具岸堤典型的斜纹层理。结果说明,猪野泽砂层先经历了风成环境,后期转向湖相沉积,也有少部分砂是通过河流沉积于剖面位置;剖面砂层与岸堤砂层的成因相似,但剖面所在位置并非湖泊岸堤;剖面砂层形成时期风沙活动强烈,湖泊水动力条件稳定,河流对湖泊影响较小。     

Ancient and modern cold-climate aeolian sand deposition: A review

Although partly active aeolian sand sheets and dunes cover large areas in the zones of (dis)continuous permafrost, little precise information is available about the influence of cold-climate conditions on modern aeolian processes. This means that palaeoenvironmental reconstructions in the stabilised, mainly Late Pleistocene dune fields and cover sand regions in the ‘sand belts’ of the European Lowlands and the Northern Great Plains of the USA and Canada, are necessarily still based on ancient evidence. Cold-climate wind deposits are typically derived from areas of abundant sediment supply like unvegetated flood plains, glacial outwash plains, till plains and lake shores. The common parabolic and transverse dune forms resemble those observed in temperate regions. Although a variety of periglacial features has been identified in Late Pleistocene dune and cover sands none of them indicate that permafrost is crucial to aeolian activity. Specific structures in aeolian strata permit tentative interpretation of the moisture content of depositional sand surfaces, the nature of annual sedimentation cycles and the processes by which strata were deposited and/or contorted. But surprisingly little is known about the role of vegetation in the process of sand accumulation. Dunes are most informative with respect to reconstructions of past wind regimes, which offer important data for verification of palaeoclimatic simulations.     

Developmental characteristics of aeolian dunes and environmental changes in the adjoining region of Puruogangri ice sheet, North Tibetan Plateau

A large area of moraine sediments and cryogenic weathering products, formed by glacial action and a cold environment, are the main source of aeolian sand in the high and cold region of the Qinghai–Tibetan Plateau in China. The evolution of aeolian dunes is closely related to the periglacial environment. Owing to the freezing of dune-land surfaces, the evolution of sand dunes is dominated by expanding dune bases and vertical accretion, thereby forming large barchan dunes. The migration rates of these large barchan dunes are very slow at an average rate of 1.7–0.7 cm·a^–1. The temperature mainly controls the environmental changes in the adjoining region of Puruogangri ice sheet. The ¹⁴C dating of humus layers in the studied area of the sand dune are 10,780±130, 9,549±130, 8,320±110, 7,450±100, 5,970±95, 5,330±90, 4,420±80, 3,460±80, 2,280±70, 980±70 aBP, respectively. The regions high temperature rising up during summer from the southwest monsoon intensity might be an important factor. As long as both water and temperature conditions are suitable, the plants will grow well, sand dunes will be stabilized, forming humus layers. Otherwise, sand dunes are bare and re-activate.     

Textural characteristics and genesis of the aeolian sediments in the Kuwaiti desert

Several types of aeolian deposits have been recognized in Kuwait: (a) smooth sand sheets that resemble desert floor sand, (b) immobile sands that include rugged vegetated sand sheets and wadi fill deposits, and (c) mobile sands that form active sand sheets and sand dunes. Simple size frequency curves illustrate the genetic relationship between the various aeolian sediment types. The four size parameters, namely, mean size, sorting, skewness and kurtosis, were calculated. Scatter plot diagrams of sorting versus mean size and sorting versus kurtosis are effective in differentiating smooth sand sheet deposits from dune sands. Active sand sheet deposits can also be recognized because they are usually located between the two end members–smooth sand sheets and dune sands. Size parameters change with location regardless of their types. Coarsening and positive skewness usually increase downwind. Mineralogical and textural characteristics of the aeolian deposits in Kuwait revealed that they are mostly derived from the lower Mesopotamian muddy flood plain deposits, the sand fraction of the Al-Dibdibba gravelly deposits and the disintegrated material from calcretic and gypcretic duricrusts. Distribution of depositional and deflational areas indicates that the northern desert of Kuwait is characterized by a positive sand budget, whereas the southern desert has a negative sand budget.     

The effects of the last glacial paleo-aeolian sands on desertification in northern China

In this paper, nine sediment sequences in the inner desert, desert-loess transitional zone (agro-pastoral transitional zone) and the northern margin of the Loess Plateau were investigated to study the sediments of Mu Us (Maowusu) and Otindaq (Hunshandake) sandy land in northern China since the last glaciation. All of these sequences consisted of the upper Holocene dark paleosol and the lower aeolian sand formed during the last glacial stage. The Mu Us and Otindaq sandy land became the active desert since the last glaciation and covered a larger sandy area than at present. Mu Us sandy land began to show a landform of sandy desert and expanded southward towards the northern boundaries of the Loess Plateau. The Holocene was characterized by the advent of warmer and wetter climatic conditions in northern China, resulting in the rapid growth of surface vegetation and Mu Us and Otindaq sandy land became a steppe. The thickness of surface soil reached up to as much as 50–80 cm. Thick paleosol covered the drift sands, and served as a protective layer for the steppe and farmland. Although the last glacial cycle is far away, paleo-aeolian sands formed during that period are still the material sources of regional desertification. Unreasonable cultivation destroying the Holocene paleosol, combined with dry climate and strong wind would result in activation of paleo- aeolian sand leading to the desertification of the study areas.